The present invention relates to a sputtering system which is a kind of thin film deposition system.
The sputtering system is a system for depositing a thin film by a method comprising generating plasma by producing gas discharge generally in a low vacuum atmosphere and making cations of the plasma collide against a target set on a negative electrode that is called a sputtering electrode, so that particles sputtered by the collision are deposited onto the substrate. This sputtering system, in which the control of thin film composition and the operation of the system are relatively easy, has been used widely for a film deposition process.
FIG. 7 shows the construction of a conventional magnetron sputtering system. Referring to FIG. 7, reference numeral 101 denotes a vacuum vessel, 102 denotes an evacuation port, through which evacuation is made by a vacuum pump (not shown), and 103 denotes a movable valve, which allows evacuation conductance to be controlled. The object denoted by numeral 104 is a main valve.
Numeral 105 denotes a gas inlet tube directed toward the inside of the vacuum vessel 101, and 106 denotes a gas flow rate controller attached to the gas inlet tube 105. Numeral 107 denotes discharge gas, which is introduced into the vacuum vessel 101 through the gas inlet tube 105, and argon gas is normally used. Numeral 108 denotes a gas inlet valve.
Numeral 109 denotes a target, 110 denotes a sputtering electrode, 111 denotes a power supply for discharge, and 112 denotes a magnet, which is arranged at the rear surface side of the target 109. Numeral 113 denotes a substrate holder disposed within the vacuum vessel 101 so as to be opposed to the front surface of the target 109, and a substrate 114 for depositing a thin film is set on the substrate holder 113. The object denoted by 118 is an insulator.
With respect to the sputtering system constructed as shown above, its operation is described below. First, the interior of the vacuum vessel 101 is evacuated to about 10xe2x88x927 Torr through the evacuation port 102 by the vacuum pump. Next, the discharge gas 107 is introduced into the vacuum vessel 101 via the gas inlet tube 105 connected to one end of the vacuum vessel 101, so that the internal pressure of the vacuum vessel 101 is maintained at about 10xe2x88x92-3 to 10xe2x88x922 Torr. In this state, power is supplied from the DC or high-frequency discharge power supply 111 to the sputtering electrode 110 to which the target 109 is mounted, so that an electric field is formed. As a result, by the action of the electric field in combination with a magnetic field due to the magnet 112 set on the rear side of the target 109, ring-shaped plasma due to discharge occurs near the surface of the target 109, giving rise to a sputtering phenomenon. Thus, by sputtered particles emitted from the target 109, a thin film is deposited on the substrate 114 set on the substrate holder 113.
In recent years, as the thin film material progressively advances to higher functions, there is a growing need for film deposition under low gas pressure. In the case of film deposition under about 10xe2x88x923 Torr or lower pressure, the above magnetron sputtering system would be problematic in discharge stability, so would be substantially difficult to achieve the film deposition.
Therefore, as described in Japanese Laid-open Patent Publication No. 6-041739, there has been an attempt made in which a helical coil connected to a high-frequency power supply is provided between a substrate and a target of the magnetron sputtering system so as to stabilize the discharge under low g as pressure. The coil generates an inductive magnetic field when high-frequency power is applied thereto. FIG. 8 shows a schematic construction of a magnetron sputtering system in which this helical coil is additionally provided. Referring to FIG. 8, numeral 121 denotes the helical coil. Numeral 122 denotes a coil-use high-frequency power supply connected to the helical coil 121. T his magnetron sputtering system operates generally in the same way as the foregoing magnetron sputtering system, but differs therefrom in that power is supplied to the sputtering electrode 110 while high-frequency power is supplied to the helical coil 121 with the coil-use high-frequency power supply 122.
As to dry etching systems, on the other hand, there have been devised some forms of discharge suitable for discharge at low gas pressure by other methods. As an example, the present applicant has previously proposed a dry etching system. In this dry etching system, as shown in FIG. 9, with a flat type antenna 131 disposed outside a vacuum vessel 101, a high-frequency power of about 50 MHz-3 GHz is applied to this flat type antenna 131 with a high-frequency power supply 135, and an electromagnetic wave generated by the flat type antenna 131 is introduced into the vacuum vessel 101 through an electromagnetic-wave inlet window 134. Also, high-frequency power is supplied from a high-frequency power supply 132 to the substrate 114, and etching gas 133 is introduced into the vacuum vessel 101 through the gas inlet tube 105, by which plasma is formed inside the vacuum vessel 101 under low gas pressure.
However, with such a constitution as shown in FIG. 8, since the helical coil 121 is set in the vacuum vessel 101, the coil material is sputtered to form in-film impurities. Also, if the coil material is prevented from being sputtered, film would be deposited on the coil, resulting in an unstable plasma. This would make a dust generating source or cause the issue of unstable plasma, disadvantageously.
Also, with such a constitution as shown in FIG. 9, in applications to a sputtering system, especially when an electrical conductor film is formed, there would occur an issue unique to a film deposition system such as a sputtering system in which the conductor film would be deposited onto the electromagnetic-wave inlet window 134, so that electromagnetic waves could no longer be radiated into the vacuum vessel 101.
In view of these issues of the prior art, an object of the present invention is to provide a sputtering system which is capable of maintaining discharge stably even under low gas pressure and thus forming a high-quality film.
In accomplishing these and other aspects, according to a first aspect of the present invention, there is provided a sputtering system comprising: a vacuum chamber; and a sputtering electrode provided in the vacuum chamber. A target is supported on the sputtering electrode with a front surface of both the target and a substrate disposed in the vacuum chamber arranged so as to be opposed to each other. In addition, a high-frequency or DC power source is provided for supplying a high-frequency or DC power to the sputtering electrode to generate plasma on the target, and an antenna is provided for generating an electromagnetic wave which is provided outside the vacuum chamber and near the target. Finally, an electromagnetic-wave inlet window is provided for introducing into the vacuum chamber an electromagnetic wave generated from the antenna which is provided in a wall of the vacuum chamber.
Thus, the sputtering system is capable of maintaining discharge stably, and so forming a high quality film, even under low gas pressure by introducing into the vacuum chamber the electromagnetic wave derived from the antenna without causing occurrence of impurities by the antenna being sputtered or causing unstable plasma due to film deposition.
According to a second aspect of the present invention, there is provided a sputtering system according to the first aspect, wherein the electromagnetic-wave inlet window is disposed on a side and rear of the target in the wall of the vacuum chamber. Thereby, the amount of film deposition onto the inner surface of the electromagnetic-wave inlet window can be lessened, and a stable film deposition can be achieved even during a continuous use.
According to a third aspect of the present invention, there is provided a sputtering system according to the first or second aspect, wherein the electromagnetic-wave inlet window is made of an insulator. Thus, since the electromagnetic-wave inlet window can electrically insulate the sputtering electrode and the vacuum chamber from each other, there is no need for providing the electromagnetic-wave inlet window implemented for introduction of an electromagnetic wave, and film deposition onto the insulator that would obstruct the introduction of an electromagnetic wave can substantially be eliminated.
According to a fourth aspect of the present invention, there is provided a sputtering system according to any one of the first to third aspect, wherein the vacuum chamber, an electromagnetic-wave transmission path comprising a space that does not maintain discharge is provided so as to range from the electromagnetic-wave inlet window to near the front surface of the target. Thus, even if the electromagnetic-wave inlet window is provided rearward, that is, on a side and rear of the target in the wall of the vacuum chamber, the electromagnetic wave can be transmitted securely to the vicinity of the target through the electromagnetic-wave transmission path, and plasma does not occur in the electromagnetic-wave transmission path so that film deposition on the electromagnetic-wave inlet window can substantially be eliminated. Thus, continuous film deposition can be achieved without replacing or cleaning the electromagnetic-wave inlet window.
According to a fifth aspect of the present invention, there is provided a sputtering system according to the fourth aspect, wherein the space of the electromagnetic-wave transmission path is a gap of 1 mm-5 mm.
According to a sixth aspect of the present invention, there is provided a sputtering system according to any one of the first to third aspects, further comprising a ground shield provided on a side and rear of the target. The ground shield and a side surface of the target define an electromagnetic-wave transmission path ranging from the electromagnetic-wave inlet window to a vicinity of a surface of the target surface opposite to the substrate formed by a space which does not maintain discharge.
According to a seventh aspect of the present invention, there is provided a sputtering system according to the sixth aspect, wherein the gap between the side surface of the target and the ground shield is set to 1 mm -5 mm.
According to an eighth aspect of the present invention, there is provided a sputtering system according to any one of the first to seventh aspects, wherein a magnet for forming a magnetic field gradient from the electromagnetic-wave inlet window toward the target is set outside the vacuum chamber so as to introduce the electromagnetic wave radiated from the electromagnetic-wave inlet window to the vicinity of the target by action of a magnetic field having the magnetic field gradient. Thus, the electromagnetic wave can be led to the vicinity of the target efficiently by action of the magnetic field having the magnetic field gradient. As a result, the electromagnetic wave efficiently acts upon the plasma generated on the target so that the discharge gas pressure can be further lowered.
According to a ninth aspect of the present invention, there is provided a sputtering system according to the eighth aspect, wherein the magnet is an electromagnetic set outside the vacuum chamber.
According to a tenth aspect of the present invention, there is provided a sputtering system according to the eighth aspect, wherein the magnet is a permanent magnet set outside the vacuum chamber.
According to an 11th aspect of the present invention, there is provided a sputtering system according to any one of the first to eighth aspects, wherein a sputtering-use magnetic circuit for generating a magnetic field that causes plasma to be trapped on the target is provided in the vicinity of the target.
Thus, as in the foregoing cases, a high-quality film deposition can be achieved even during low gas pressures. In addition, due to the magnetic field generated by sputtering-use magnetic circuit, plasma generated on the target is trapped on the target by a combination of the magnetic field and a negative potential developed at the sputtering electrodes. Therefore, the plasma density is improved, and the introduced electromagnetic wave can be led onto the target efficiently. As a result, the discharge gas pressure can be further lowered.
According to a 12th aspect of the present invention, there is provided a sputtering system according to the 11th aspect, wherein the sputtering-us magnetic circuit is provided on the front surface side of the target.
According to a 13th aspect of the present invention, there is provided a sputtering system according to the 11th aspect, wherein the sputtering-use magnetic circuit is provided on a rear surface side of the target.
According to a 14th aspect of the present invention, there is provided a sputtering system according to any one of the first to 13th aspects, wherein a high-frequency power of a 50 MHz-3 GHz frequency is supplied to the antenna set outside the vacuum chamber. As a result, the high-frequency or DC power is supplied to the target while an electromagnetic wave is radiated into the vacuum chamber via the electromagnetic-wave inlet window provided on the side and rear of the target in the wall of the vacuum chamber.
Thus, the sputtering system is capable of maintaining discharge stably, and so forming a high quality film, even under low gas pressure. In addition the electromagnetic-wave inlet window is provided on the side and rear of the target in the wall of the vacuum chamber. Thus, the amount of film deposition on the inner surface of the electromagnetic-wave inlet window can be lessened, and stable film deposition can be achieved even during continuous use.
According to a 15th aspect of the present invention, there is provided a sputtering system according to any one of the first to 14th aspects, wherein the antenna is a spiral-shaped antenna.
According to a 16th aspect of the present invention, there is provided a sputtering system according to any one of the first to 14th aspects, wherein the antenna is a flat-shaped antenna.
According to a 17th aspect of the present invention, there is provided a sputtering system according to any one of the first to 16th aspects, wherein the target is a material of an electrical conductor to be formed on the substrate.